1. Field of the Invention
The present invention relates to a novel olefin polymerization catalyst and a method for polymerizing an olefin using the catalyst. More particularly, the present invention is concerned with a novel olefin polymerization catalyst comprising: (A) a transition metal compound comprising a transition metal having xcex7-bonded thereto a cyclic anionic ligand; (B) a mixture of (B-1) an activator compound and (B-2) a specific organometal compound containing an element selected from elements of Groups 1 to 15 of the Periodic Table, the activator compound (B-1) comprising a cation and a noncoordinating, compatible anion and being capable of reacting with the transition metal compound (A) to form a metal complex having a catalytic activity; (C) a solid component having substantially no hydroxyl group; and optionally (D) an organoaluminum compound, wherein the catalyst is obtained by contacting components (A) to (C) and optionally component (D). The olefin polymerization catalyst of the present invention is advantageous not only in that it has high polymerization activity, but also in that an olefin polymer having excellent powder characteristics can be produced by suspension polymerization (slurry polymerization) or gaseous phase polymerization, while preventing the occurrence of adherence of the polymer to the inner wall, agitation blades and the like of a polymerizer. By virtue of such excellent properties, the catalyst of the present invention enables an olefin polymer having excellent powder characteristics to be efficiently produced by a continuous operation of a commercial scale plant. The olefin polymer produced by using the catalyst of the present invention can be advantageously used for producing various articles, such as films, molded articles (such as blow-molded articles, injection-molded articles and rotomolded articles), fibers, pipes, and coating or jacketing materials for electric transmission cables or wires. The present invention is also concerned with a method for producing an olefin homopolymer or olefin copolymer by using this catalyst.
2. Prior Art
Ziegler-Natta catalysts comprising a titanium compound and an organoaluminum compound have been widely known as a catalyst for producing olefin homopolymers and olefin copolymers.
On the other hand, it has recently been found that when a catalyst system comprising a solvent-soluble transition metal compound containing a halide, such as bis(cyclopentadienyl)zirconium dichloride, and an aluminoxane, which is one type of organoaluminumoxy compound, is used for homopolymerization of ethylene or copolymerization of ethylene with an xcex1-olefin, the catalyst system exhibits high polymerization activity. With respect to the details of this technique, reference can be made to, for example, Examined Japanese Patent Application Publication No. 4-12283 (corresponding to DE 3127133.2).
In Unexamined Japanese Patent Application Laid-Open Specification Nos. 60-35006, 60-35007 and 60-35008 (each corresponding to U.S. Pat. No. 4,937,299), it has been proposed to use, as the transition metal compound component of the above catalyst system comprising a transition metal compound and an aluminoxane, a mixture of at least two metallocenes or a substituted metallocene, so as to control the molecular weight and molecular weight distribution of a final ethylene polymer or to improve the copolymerizability of ethylene with an xcex1-olefin.
The catalyst systems proposed in the above-described prior art documents, each comprising a transition metal compound and an organoaluminumoxy compound, are soluble in a polymerization solvent. Therefore, difficult to securely support such a catalyst system on a carrier by a conventional catalyst-supporting method, for example, a method in which both a solution of the catalyst system and a dispersion obtained by dispersing a carrier in a non-solvent for the catalyst system are provided, and the solution of the catalyst system is added to the dispersion containing the non-solvent for the catalyst system, thereby causing the catalyst system to be precipitated and supported on the carrier. When such a catalyst system supported on a carrier by a conventional carrier-supporting method is used in a suspension polymerization or gaseous phase polymerization, a problem arises in that the catalyst system is caused to separate from the carrier during the polymerization so that, as well-known in the art, the catalyst system which has separated from the carrier disadvantageously produces an indefinite form of polymer, rendering it difficult to handle the polymer. Thus, only a polymer having poor powder characteristics is produced. Further, during the polymerization, such an indefinite-form polymer tends to easily adhere to various inside surfaces associated with the polymerizer, such as the inner wall of the polymerizer, the agitation blades, the outer wall of the thermometer and the like, thus forming polymer scales adhering to such inside surfaces. In addition, a part of the catalyst system which has separated from the carrier adheres to the above-mentioned various inside surfaces associated with the polymerizer during the polymerization, so that a polymerization occurs at such inside surfaces, thus forming polymer scales adhering to such inside surfaces. As well-known in the art, the adhesion of the polymer scales to the inside surfaces associated with the polymerizer poses serious problems in that excess heat cannot be efficiently removed from the polymerizer, that the agitation efficiency of the agitation blades is lowered, and that the reaction temperature cannot be accurately measured with the thermometer. These problems make it impossible to continuously perform the polymerization. Therefore, such catalyst systems (comprising a transition metal compound and an organoaluminumoxy compound) cannot be used for commercial scale production of olefin polymers by suspension polymerization or gaseous phase polymerization. Accordingly, the use of these catalyst systems is inevitably limited to a solution polymerization process. However, a solution polymerization process has a problem in that when it is attempted to produce a polymer having a high molecular weight by solution polymerization, the viscosity of the solution of the polymer is considerably increased, so that the productivity of the process becomes very low. Therefore, these catalyst systems are disadvantageous in that commercial application of them is very difficult.
In order to solve the above-mentioned problems, it has been attempted to polymerize an olefin by suspension polymerization or gaseous phase polymerization, using a catalyst comprising a porous inorganic oxide as a carrier, such as silica, alumina or silica-alumina and, carried thereon, at least one compound selected from the group consisting of a transition metal compound and an organoaluminumoxy compound.
For example, Unexamined Japanese Patent Application Laid-Open Specification Nos. 60-106808 and 60-106809 (both of which correspond to EP 0142143) disclose a method in which a first filler is contacted with a highly active catalyst component comprising a hydrocarbon solvent-soluble titanium compound and/or a hydrocarbon solvent-soluble zirconium compound, thereby obtaining a contact-treatment product, and ethylene is homopolymerized or copolymerized with an xcex1-olefin in the presence of not only the above-mentioned contact-treatment product; but also an organoaluminum compound, and a second filler having an affinity to a polyolefin which affinity is equal to or higher than that of the first filler, to thereby obtain a composition comprising an ethylene polymer and the first and second fillers.
However, in this method, it is impossible to strongly bond the highly active catalyst component to the filler, so that not only is the catalyst activity low, but also the obtained ethylene polymer has poor powder characteristics. In addition, in this method, the obtained polymer is inevitably caused to contain fillers, irrespective of whether or not it is intended to incorporate the fillers into the polymer.
Unexamined Japanese Patent Application Laid-Open Specification No. 61-31404 (corresponding to DE 3424697.5) discloses a method in which ethylene is homopolymerized or copolymerized with an xcex1-olefin in the presence of a catalyst comprising a mixture of a transition metal compound, and an organoaluminumoxy compound-carrying substance obtained by contacting a water-containing inorganic substance with an organoaluminum compound, such as trialkylaluminum.
However, when a water-containing inorganic substance is contacted with an organoaluminum compound, only the water in the water-containing inorganic substance is reacted with the organoaluminum compound to form a reaction product, which is not chemically bonded to the inorganic substance, so that the formed reaction product cannot be securely carried on the inorganic substance. Further, the reaction between water and the organoaluminum compound is a vigorous exothermic reaction and hence it is very difficult to synthesize only an organoaluminumoxy compound selectively while controlling the molecular weight of the organoaluminumoxy compound to an appropriate level, so that it is difficult to obtain an organoaluminumoxy compound having a molecular weight in the range which is effective for facilitating polymerization. Therefore, this method cannot be effectively put to practical use.
Unexamined Japanese Patent Application Laid-Open Specification No. 4-224808 discloses a method for xcex1-olefin polymerization using a solid catalyst. The solid catalyst is obtained by contacting aluminoxane with an inorganic compound containing water of crystallization or having water adsorbed thereon, to thereby obtain a solid product, and subsequently contacting the obtained solid product with a metallocene compound and, optionally, an organometal compound. Further, Unexamined Japanese Patent Application Laid-Open Specification No. 6-145238 discloses a method for the polymerization of olefins, using a solid catalyst. The solid catalyst is obtained by contacting and reacting aluminoxane with an inorganic oxide containing no water or having adsorbed thereon not more than 10% by weight of water, to thereby obtain a solid auxiliary catalyst comprising the inorganic oxide having the aluminoxane carried thereon, and contacting the obtained solid auxiliary catalyst with a transition metal compound and an organoalkylaluminum compound to prepare a solid catalyst, which is used immediately upon preparation thereof. However, in these methods, the aluminoxane cannot be securely carried on the inorganic solid. When such an aluminoxane-carrying inorganic solid is used as a catalyst, the aluminoxane disadvantageously is caused to separate from the inorganic solid during the polymerization. The separated aluminoxane is reacted with a metallocene compound to form a complex having a polymerization activity, which complex disadvantageously causes formation of a polymer having an indefinite form but not having a desired form, such as a particulate form. As described above, such an indefinite-form polymer is likely to adhere to the inner wall and the like of the polymerizer. Thus, these methods cannot take full advantage of the use of a catalyst carried on a carrier. Therefore, it is difficult to commercially use these methods.
Unexamined Japanese Patent Application Laid-Open Specification Nos. 60-35006, 60-35007 and 60-35008 have a description to the effect that a transition metal compound and an organoaluminumoxy compound may be carried on a carrier, such as silica, alumina or silica-alumina, and the resultant product can be used as a catalyst. Unexamined Japanese Patent Application Laid-Open Specification Nos. 61-108610, 61-296008 and 5-155931 disclose a method in which an olefin is polymerized in the presence of a catalyst comprising an inorganic oxide as a carrier and, carried thereon, a transition metal compound, such as zirconocene, and aluminoxane.
However, in any of these methods, the catalyst cannot be securely carried on the carrier. Therefore, during the polymerization, the catalyst disadvantageously is caused to separate from the carrier, and the separated catalyst exhibits in situ a polymerization activity, causing the resultant polymer to be in an indefinite form. The indefinite-form polymer is likely to adhere to the inner wall of the polymerizer, the agitation blades, the baffle plates and the like, thus making it impossible to continuously perform the polymerization on a commercial scale. Unexamined Japanese Patent Application Laid-Open Specification No. 63-280703 (corresponding to EP 0294942) discloses an olefin polymerization catalyst comprising an organometal compound, a particulate carrier, aluminoxane, a compound containing a transition metal selected from the metals of Group 4 of the Periodic Table, and an olefin polymer formed by preliminary polymerization. Further, Unexamined Japanese Patent Application Laid-Open Specification No. 5-155930 discloses a method for the preliminary polymerization of an olefin, using a particulate carrier having water adsorbed thereon and having a hydroxyl group in the surface thereof, each in a specific amount.
These methods have been expected to provide advantages that the preliminary polymerization improves the powder characteristics of the final polymer and that a polymer formed by the preliminary polymerization protects the catalyst containing a transition metal compound and an organoaluminumoxy compound and prevents the catalyst from being deactivated with time. However, although the powder characteristics of the polymer are improved to some extent, the improvement is not satisfactory. In addition, these methods have problems in that, since it is necessary to additionally involve the step of preliminary polymerization, not only is the quality of the final polymer likely to be distributed, but also the production cost of the polymer is high.
As a substituent for an aluminoxane which serves as a promoter for a metallocene catalyst system, Japanese Patent Application prior-to-examination Publication (kohyo) No. 1-502036 (corresponding to WO88/05793) and Japanese Patent Application Laid-Open Specification No. 8-34809 (corresponding to WO94/07927, U.S. Pat. No. 5,599,761 and EP 0 277 004) disclose a bulky, noncoordinating ionic promoter comprising an anion comprising a plurality of lipophilic groups covalently coordinating with and shielding a central, formal charge-bearing metal or metalloid atom. In these prior art documents, it is described that this ionic promoter is advantageous not only in that it has high polymerization activity, but also in that it can exhibit excellent copolymerizability. However, the anion of the above ionic promoter does not contain a reactive substituent, such as an alkyl group contained in an aluminoxane wherein the alkyl group can directly react with a hydroxyl group on the surface of a carrier, e.g., a silica. Hence, the above ionic promoter cannot form a chemical bond with a carrier, so that it is difficult to securely support the ionic promoter on a carrier. For supporting the ionic promoter on a carrier, it is necessary to use a method described in WO91/09882, i.e., a method which comprises subjecting a carrier to dehydration, treating the dehydrated carrier with an alkylaluminum solution to obtain an inert carrier, and physically adsorbing an ionic promoter onto the obtained inert carrier. However, by such a method, the ionic promoter cannot be securely supported on the carrier, so that, during the polymerization, the occurrence of adherence of a polymer scale to inside surfaces associated with a polymerizer cannot be prevented.
Japanese Patent Application prior-to-examination Publication (kohyo) No. 7-501573 (corresponding to WO93/11172 and U.S. Pat. No. 5,427,991) discloses a promoter which comprises a polyanionic moiety comprising a plurality of metal or metalloid atom-containing noncoordinating anionic groups which are pendant from and chemically bonded to a core component of the catalyst system. Further, WO96/28480 discloses a method in which a promoter comprising a compatible anion having a substituent containing at least one active hydrogen moiety is provided, and the promoter is caused to be supported on a carrier which has been treated with an organometal compound. The object of the techniques of the above prior art documents is to securely support a promoter on a carrier by forming a chemical bond therebetween. By using the techniques of the above prior art documents, the occurrence of adherence of a polymer scale to inside surfaces associated with a polymerizer can be prevented to some extent. However, these techniques have a defect in that, when a promoter is chemically bonded to a carrier, the chemical properties of the promoter are inevitably changed, so that the catalytic activity of the promoter supported on the carrier becomes disadvantageously low, as compared to that expected before being supported on the carrier.
As described hereinabove, the prior art techniques have problems in that it is impossible to produce an olefin polymer having excellent powder characteristics by suspension polymerization (slurry polymerization) or gaseous phase polymerization, while achieving high polymerization activity and preventing the occurrence of adherence of the polymer to the inner wall, the agitation blades and the like associated with a polymerizer.
Therefore, it has been desired to develop a novel catalyst which not only has high polymerization activity, but also enables commercial production of an olefin polymer having excellent powder characteristics, while preventing the occurrence of adherence of the polymer to the inner wall, the agitation blades and the like associated with a polymerizer.
In this situation, the present inventors have conducted extensive and intensive studies with a view toward solving the above-mentioned problems accompanying the prior art. As a result, it has unexpectedly been found that an olefin polymerization catalyst obtained by contacting several specific components is advantageous not only in that it has high polymerization activity, but also in that an olefin polymer having excellent powder characteristics can be produced by suspension polymerization (slurry polymerization) or gaseous phase polymerization, while preventing unfavorable phenomena, such as the occurrence of adherence of the polymer to various inside surfaces associated with a polymerizer. More specifically, the present inventors have unexpectedly found that the problems accompanying the prior art can be solved by the use of an olefin polymerization catalyst comprising: (A) a transition metal compound comprising a transition metal having xcex7-bonded thereto a cyclic anionic ligand; (B) a mixture of (B-1) an activator compound and (B-2) a specific organometal compound containing an element selected from elements of Groups 1 to 15 of the Periodic Table, the activator compound (B-1) comprising a cation and a noncoordinating, compatible anion and being capable of reacting with the transition metal compound (A) to form a metal complex having a catalytic activity; (C) a solid component having substantially no hydroxyl group; and optionally (D) an organoaluminum compound, wherein the catalyst is obtained by contacting components (A) to (C) and optionally component (D). By the use of such a catalyst, in which a catalytically active species formed by the reaction between components (A) and (B-1) is very securely supported on carrier component (C) due to the action of component (B-2) not by chemical bonding, but by physical adsorption, to thereby prevent a separation of the catalyst active species from the carrier component, an olefin polymer having excellent powder characteristics can be efficiently produced by a continuous operation of a commercial scale plant, while preventing unfavorable phenomena, such as the occurrence of adherence of the polymer to various inside surfaces associated with a polymerizer. The present invention has been completed, based on the above novel finding. Accordingly, it is an object of the present invention to provide an olefin polymerization catalyst, especially an ethylene polymerization catalyst, which is advantageous in that it not only has high polymerization activity, but is also capable of producing an olefin polymer having excellent powder characteristics by suspension polymerization (slurry polymerization) or gaseous phase polymerization, while preventing unfavorable phenomena, such as the occurrence of adherence of the polymer to various inside surfaces associated with the polymerizer, thereby enabling an olefin polymer having excellent powder characteristics to be efficiently produced by a continuous operation of a commercial scale plant.
It is another object of the present invention to provide a method for effectively and efficiently producing an ethylene homopolymer or an ethylene copolymer in the presence of the catalyst of the present invention.
The foregoing and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description taken in connection with the appended claims.